Vehicles commonly have an engine and a battery for storing a charge used to start the engine. In hybrid electric vehicles, the battery may also be used to power one or more electric motors. Generally, an idle battery will lose its charge over time. This is generally not a concern for drivers who use their vehicle on a regular basis because almost all vehicles contain a battery charging system to recharge the battery while driving.
But it is possible for a battery to remain idle too long so that it reaches a charge level, known as a state of charge, that is too low to start the engine. For example, a battery in a vehicle parked for many weeks may reach a state of charge too low to start the vehicle. Likewise, a newly manufactured vehicle may be shipped a long distance, such as overseas, allowing the sate of charge of the battery to drop too low to start the vehicle at its destination. Therefore, it may be desirable to increase the time that a battery remains idle yet provides sufficient power to start the engine after that time.
Likewise, some vehicle operations, such as racing a hybrid electric vehicle or providing electrical power to on-board or off-board electrical equipment, require a level of electrical charge greater than that required for normal vehicle operation. Therefore, it may be desirable to increase the amount of power available from the battery for those operations.